1. Field of the Invention
The present invention relates to a biaxially stretched polylactic acid multilayer film useful as a packaging film, which is furnished with biodegradable property and is excellent in transparency, optical characteristics such as gloss, and low temperature heat sealability as well as the use thereof. More particularly, the present invention relates to a biaxially stretched polylactic acid multilayer film wherein a biaxially stretched film substrate is coated on at least one surface thereof with a biodegradable coating layer comprising an aliphatic polyester composition as well as the use thereof as packaging materials.
2. Description of the Prior Art
In recent years, biodegradable films have attracted public attention with a view to facilitating disposal treatment of plastic films, and as a result, various kinds of films have been developed hitherto. These biodegradable films undergo hydrolysis and/or biodegradation in soil or water, while gradually permitting decomposition and disintegration of the films, and finally these films are converted into harmless decomposition products by the aid of microorganisms. Known as such films are those made of aromatic polyester resins, aliphatic polyester resins such as polylactic acid and polybutylene succinate, polyvinyl alcohol, cellulose acetate, and starch.
A biaxially stretched film comprised of polylactic acid which is one of such biodegradable resins excels in transparency and so is commenced to use as a packaging film. However, this film is devoid of heat sealable property as such. As a means for imparting heat sealable property to biaxially stretched polylactic acid films, there are proposed (1) a biaxially stretched laminated film of polylactic acid type (JP-A-2001-219522, claim 1) manufactured by laminating one surface of a biaxially stretched film of polylactic acid with a polymer of polylactic acid series containing predominant amount of D-lactic acid and (2) a multilayer biodegradable plastic film (JP-A-8-323946, claim 1) manufactured by laminating one surface of a biaxially stretched film comprising polylactic acid with an aliphatic polyester having a low melting point such as 1,4-butanediol succinate. However, these laminated films are poor in the quality as packaging films since they are inferior in low temperature heat-sealability or optical characteristics, even if they are furnished with heat-sealability.
In the aforesaid circumstances, therefore, there is a demand for developing a novel polylactic acid multilayer film possessing not only biodegradability but also excellent transparency and gloss.